1. Field of the invention:
This invention relates to an electrostatic coating machine and a method of changing color of paints thereby, and more particularly, relates to an electrostatic multi-color coating machine for coating a plurality of articles with paints of different colors, which is capable of rapid cleaning of a rotary atomizing head, paint feed and drain passages and the like after the end of coating the preceeding article with a preceeding or last color and, accelerating the coating preparation for the succeeding article with a succeeding or next color, as well as a method of changing color of paints in such a coating machine.
For coating articles, for example, continuously sent on a conveyor arranged at a predetermined interval, it is required to change the color of paints in the electrostatic coating machine where different coating colors are to be applied on one article and the other article succeeding thereto. Such color change has conventionally been carried out by a method of bringing a cleaning shroud around a rotary atomizing head after the coating has been completed for the preceeding article, supplying cleaning fluids consisting of air, thinner and the like from a cleaning source to clean the paint feed passage, the rotary atomizing head and the like, thereby forcing the used cleaning fluid or drainage to flow into the cleaning shroud and then discharging the fluid by way of a drain pipeway. The paint of the succeeding color has also been supplied in the same manner as above by feeding the paint to the rotary atomizing head.
However, in changing the paint color by the prior art method referred to above, the cleaning fluid and the paint have to be supplied at low speed and low pressure in small flow rate so that the cleaning liquid or the paint should not scatter from the rotary atomizing head nor overflow from the shroud to the outside to otherwise result in circumferential contaminations. Thus, such a prior art method has a defect in that much time is taken for the cleaning and the coating preparation.
Further, in a case where the paint which contains metal powder such as of aluminum (hereinafter referred to as a metallic paint) is used for the coating, metal powder remained in the drain pipe causes to ground the high voltage to the earth by bridging the same in the drain pipe which produces electro-conductor therein. Thereby, sparks are generated to cause the danger of fire accidents. Therefore, the drain pipe has to be cleaned by way of the cleaning shroud in the prior art method, thus resulting in further extended time being required therefor.
2. Object of the invention:
Accordingly, an object of this invention is to provide an apparatus and a method capable of rapidly changing the color of paints in an electrostatic coating machine.
Another object of the present invention is to provide an apparatus and a method in which the paint feed passages are divided into major portions from color change valve mechanisms in close proximity to a rotary atomizing head and the remaining minor portion and in which cleaning and coating preparation can be carried out portionwise for such divided portions, the rotary atomizing head and the drain passage successively.
A further object of this invention is to provide an apparatus and a method capable of decreasing those portions which the cleaning fluid is to be fed at a low pressure in a low flow rate as much as possible, and thereby feeding the cleaning fluid at a high pressure in a great flow rate for the major portion of the paint feed passage which forms the most part to be applied cleaning fluid.
A still further object of this invention is to provide an apparatus and a method of changing paint color in an electrostatic coating machine, capable of preventing the cleaning fluid or the paint from overflowing out of the cleaning shroud and also capable of preventing the drain pipe from generating an electro-conductivity by bridging the metal contained therein in a case of using metallic paint as a succeeding color.